Engine speed governors are commonly used on internal combustion engines in many different applications. Typical applications are for vehicle engines of trucks and buses. As is well known, speed governors are employed for the purposes of limiting operating speeds and for protecting the engines from damage due to overspeed.
Combined engine and load speed or road speed governors have been developed which are responsive to both engine speed and vehicle speed for controlling or limiting the engine speed. A governor of this type is disclosed in U.S. patent application Ser. No. 036,064 filed by Harry D. Sturdy on May 4, 1979. An electronic control circuit especially adapted for a governor of the type disclosed in said patent application is disclosed and claimed in my U.S. Pat. No. 4,090,480 granted May 23, 1978 and in my patent application Ser. No. 047,544 filed June 11, 1979.
In certain types of vehicles, such as dump trucks and garbage trucks, the engine is provided with a power take off (PTO) for driving an auxiliary load. In such vehicles it is desirable to provide an engine speed governing function especially adapted for the PTO operation. In particular, it is desirable to provide speed governing with a higher degree of accuracy and to provide control which will prevent damage to the power train of the vehicle.
A general objective of this invention is to provide an electronic control circuit for an engine speed governor which is especially adapted for governing an engine having a power take off.